Another concept...how bout this:
I can tell that it's a combination of os sacrum and os cocxygea forming os koxa with the asetabulum at both side (see two little round holes at each side). So, If Joker said that the length of this bone is 6 inches (sacrum + coccyx) then we'll add it with:
- os vertebrae lumbar which nearly the same with os sacrum (+/- 3 inches)
- os vertebrae thorasix (2 times longer than sacrum [+/- 6 inches])
- os vertebrae servix (1.5 times longer than sacrum [+/- 4.5 inches])

and we'll form an os vertebrae measured for 19.5 till 20 inches long. I assumed it's a back bone of an average lizard...
For the length of the other bone, it's just my expectations...

Q: Why are chemists great for solving problems?
A: They have all the solutions.

.. as I said...my professor also said that it was os koxa, combination of os sacrum and os coccyx. For the explanation, just see the hole at both side. My professor said that it wasn't a skull because if it's a skull, then those holes will be located at the back (the bigger size) and not at the middle.

Q: Why are chemists great for solving problems?
A: They have all the solutions.

It looks pretty fake to me......it is too bleached white and new looking to have been found by someone walking through the wilderness, especially one with the climate and environment of Rhode Island. Second, there is no known land animal with a skull structure like that.....sea creatures are another story, but still, i dont believe i have seen anything like that before.